c 


The  Miami  Bulletin 

Seriks  VII.  Mx\Y,  1908.  Number  1 


Teachers’  Bulletin  No.  2,  Department  of 
Agricultural  Education,  Ohio  State  Normal 
College,  Miami  University,  Oxford,  Ohio 


EXPERIMENTAL  STUDIEo 
OF  PLANT  GROWTH 

B.  M.  DAVIS 


Published  Monthly  by  Miami  University 

And  Entered  at  Postoffice^  Oxford^  Ohio,  as  Second  Class  Mail  Matter 


Work  of  the  Department  of  Agricultural  Educa- 
tion of  the  Ohio  State  Normal  College 
of  Miami  University. 


The  organization  of  this  department  began  in  January 
1907.  The  work  undertaken  is  two  fold. 

1.  To  help  teachers  and  prospective  teachers  who  may 
wish  to  make  use  of  practical  nature-study  or  ele- 
mentary agriculture  in  the  public  schools : 

(a)  By  means  of  direct  instruction  in  class- 
room and  laboratory. 

(b)  By  means  of  correspondence.  The  depart- 
ment is  often  able  to  give  helpful  suggestions  in 
answer  to  letters  of  inquiry,  especially  in  regard 
to  references  to  literature  on  special  subjects. 

(c)  By  means  of  conferences  with  teachers  and 
members  of  school  boards  as  to  plans  and  methods 
of  taking  up  the  work  in  township  schools. 

2.  To  co-operate  with  teachers  in  typical  country 
schools,  particularly  in  village  or  township  high 
schools  in  farming  communites,  to  determine  by 
actual  experiment  what  phases  of  agriculture  as  a 
school  subject  are  best  adapted  to  the  needs  of  such 
schools,  and  how  the  subject  should  be  handled  to 
the  best  advantage  under  average  country  school 
conditions. 

Efficient  instruction  in  agriculture  is  desirable  in 
small  high  schools  of  rural  districts  not  only  on  ac- 
count of  its  educational  and  practical  value,  but  also 
because  the  teaching  force  of  the  ungraded  schools 
is  chiefly  recruited  from  these  high  schools.  The 
problem  of  agricultural  instruction  in  the  village  or 
township  high  school,  therefore,  is'fdoubly  impor- 
tant, and  deserves  the  most  careful  consideration  of 
all  concerned. 


INTRODUCTION. 


'‘But  the  great  object  of  the  teachers  of  ‘science’ 
should  be  to  teach  the  art  of  experimenting  - the  meaning 
and  use  of  an  experiment.  The  essential  first  step  in  an  ex- 
periment Js  to  have  a clear  conception  of  the  motive  of  the 
quest  in  which  it  is  proposed  to  engage.”  * 

It  is  in  the  spirit  of  this  conception  of  science  teaching 
that  the  following  studies  of  plant  growth  have  been  brought 
together. 

After  considerable  observation  the  writer  is  convinced 
that  introductory  science,  and  to  a certain  extent  all  science 
as  taught  in  the  average  small  high  school  fails  to  do  more 
than  give  a certain  amount  of  scientific  information.  In 
many  schools  it  is  taught  wholly  from  text-books.  Fortun- 
ately these  text-books  are  generally  well  written,  and  the 
statements  contained  in  them  are  usually  scientifically  cor- 
rect. But  in  order  to  learn  to  make  use  of  information  from 
books  one  must  learn  from  actual  experience  how  such 
information  is  obtained. 

Science  in  the  small  high  schools  must  be  taught  by 
teachers  who  divide  their  time  with  other  subjects,  and  who 
are  sometimes  unfortunate  in  their  own  scientific  training. 
Well  equipped  laboratories  are  out  of  the  question  for  most 
of  these  schools.  Such  conditions  are  often  made  an  excuse 
for  the  inferior  character  of  work  done. 

On  the  other  hand,  bright  and  active  boys  and  girls  at- 
tend these  schools.  Many  of  these  children  come  from 
farms  where  nature  is  dealt  with  most  intimately.  They  are 
familiar  with  plant  and  animal  life,  and  are  used  to  doing 
things. 

With  such  children  to  work  with,  well  equipped  labora- 
tories land  expensive  [apparatus  are  not  needed,  at  least  for 
their  introductory  science.  The  chief  concern  is  to  get  the 
children  to  work  on  problems  which  have  to  do  with  things 
already  familiar,  and  the  solution  of  which  will  give  signifi- 
cance to  these  things. 

Such  a course  of  study  might  be  called  agriculture,  or 
botany  in  so  far  as  it  concerns  plants,  or  physics  in  so  far  as 

* Henry  E.  Armstrong,  “The  Teaching  of  Scientific  Method,”  pp. 
204-205.  New  York  : The  Macmillan  Co. 


3 


it  cmicerns  soil  and  farm  machinery.  The  name  is  unim- 
portant, but  since  agriculture  deals  fundamentally  with 
plants  and  the  soil  the  use  of  this  name  for  such  work  maybe 
desirable. 

The  v/riter  believes  work  of  the  character  just  sug- 
gested should  give  the  child  his  first  training  in  science, 
whether  in  the  later  grammar  grades  or  in  the  first  year  of 
high  school.  Such  a procedure  is  practical,  for  it  is  in  the 
reach  of  the  average  school;  it  is  also  practical  in  another 
way,  for  it  will  have  the  support  and  interest  of  the  patrons, 
it  is  pedagogical,  for  it  enlists  the  child’s  own  activities  by 
enabling  him  to  ‘Team  by  doing”;  it  is  scientinc  for  it  puts 
emphasis  on  experiment  and  correct  method  of  research, 
rather  than  upon  scientific  information. 

The  experimieiital  studies  of  “Soil  and  its  Relation  to 
Plants”  (7*)  have  been  used  by  several  small  high  schools  in 
farming  communities,  and  many  of  the  simpler  studies  have 
been  used  in  the  grammar  grades  of  similarly  situated 
schools.  The  success  of  this  work  as  indicated  by  the  inter- 
est of  the  pupils,  both  boys  and  girls,  and  of  the  parents,  has 
encouraged  the  writer  to  prepare  the  present  bulletin  deal- 
ing with  plant  growth. 

The  experim^ents  outlined  have  all  been  tried,  under  the 
writer’s  direction,  by  pupils  of  various  ages  and  capacities, 
and  seem  well  adapted  to  pupils  of  the  first  year  high  school. 

The  familar  fact  that  when  seeds  are  planted  they  will 
develop  sooner  or  later,  in  the  ordinary  course  of  events,  in- 
to plants  furnishes  a basis  for  inquiry  by  means  of  experi- 
ment. What  takes  place  from  the  time  the  seed  is  planted 
until  the  plant  appears?  When  this  question  is  resolved  into 
a series  of  questions  in  the  form  of  problems,  and  these  an- 
swered by  means  of  observation  and  experiment,  some  of  the 
most  important  facts  of  plant  growth  will  be  realized  and 
will  be  made  to  give  meaning  to  many  familiar  practices  in 
plant  propagation.  At  the  same  time,  and  yet  more  impor- 
tant, will  be  the  insight  into  and  practical  training  in  the 
scientific  method  of  inquiry.  To  develop  ability  to  use  this 
method  is,  after  all,  the  true  aim  of  science  teaching,  and 

* Note — Figures  refer  to  references  on  pp.  31. 


4 


science,  in  the  words  of  an  eminent  scientist,  is  but  “human 
experience  tested  and  put  in  order. 

The  exercises  in  plant  growth  outlined  in  this  bulletin 
have  been  adapted  from  various  sources.  Some  of  the  experi- 
ments are  classical  in  plant  physiology  and  appear  with  cer- 
tain modifications  in  all  text-books  dealing  with  the  subject. 

The  writer  wishes  to  acknowledge  the  helpful  sugges- 
tions v/hich  he  has  received  from  “Plant  Production”  by  D. 
J.  Crosby,  “Beitraege  ZurMethodik  des  Botanischen  Unter- 
richts”  by  F.  Schleichert,  and  especially  from  “Experiments 
with  Plants”  by  Dr.  W.  J.  V.  Osterhout.  The  figures  which 
contribute  greatly  to  the  clearness  of  many  of  the  exercises 
have  all  been  taken  from  “Experiments  with  Plants.”  For 
kindly  permitting  him  to  use  these,  the  writer  is  indebted  to 
Dr.  Osterhout  and  to  The  Macmillan  Co. 

Suggestions  to  Teachers  as  to  Method. 


In  pursuance  of  the  general  plan  already  indicated,  the 
following  exercises  are  intended  to  persenta  series  of  simple 
experiments  dealing  with  plant  growth.  Following  the  pre- 
liminary exercises  I to  V,  the  solution  of  each  problem 
usually  presents'another  for  investigation. 

The  title  of  each  exercise  is  a statement  of  the  subject 
to  be  studied  by  means  of  experiment.  This  is  followed  by 
a brief  account  of  how  to  conduct  the  experiment  or  experi- 
ments in  order  to  find  an  answer  to  the  problem  suggested  in 
the  title. 

It  is  important  that  the  pupil  should  have  a clear  concep- 
tion of  the  problem  and  some  directions  as  to  how-to  proceed 
in  its  solution.  His  success  will  depend  upon  the  clearness 
of  his  conception  of  what  he  is  to  find  out,  and  also  upon  the 
faithfulness  with  which  he  carries  out  the  details  of  the  ex- 
perim.ent.  In  order  better  to  insure  this,  each  pupil  should 
keep  a record  of  what  he  undertakes. 

Such  a record  should  contain : 

1.  Statement  of  the  problem  or  object  of  the  exercise  or 
experiment. 

2.  Statement  of  the  material,  apparatus,  etc.,  used. 

3.  Statement  of  the  procedure  in  workng  out  the  problem 


or  experiment.  This  will  include  setting  up  of  apparatus, 
if  any  is  used,  and  may  be  illustrated  by  diagrams. 

4.  Observations.  A careful  record  of  observations 
should  be  made,  including  time  of  observation  (day  and 
hour) . 

5.  Statement  of  results.  This  is  a sort  of  final  sum- 
mary of  observations. 

6.  Conclusions.  Sometimes  this  and  (5)  may  be  includ- 
ed in  one  statement. 

A great  deal  depends  upon  the  care  of  experiments.  As 
most  of  the  exercises  will  be  concerned  with  living  plants  or 
seeds  it  is  necessary  to  make  daily  observations  in  order  (a) 
to  note  the  progress  of  the  experiment  and  (b)  to  see  that 
the  conditions  are  kept  favorable,  especially  as  to  moisture 
and  warmth  v/here  these  are  concerned.  The  habit  of  clear- 
ing up  the  experiment  as  soon  as  it  is  finished  should  be  en- 
couraged. By  this  is  meant  cleaning  bottles,  jars,  dishes, 
etc.,  and  putting  away  apparatus  no  longer  needed. 

All  material  and  apparatus,  and  also  reference  books  and 
pamphlets  should  be  provided  as  far  as  possible  by  the  time 
the  course  is  begun.  Some  of  the  material  for  exercises  will 
require  preparation  by  the  teacher  sometime  in  advance  of 
the  work  by  the  pupil.  As  soon  as  the  work  is  fairly  begun 
by  the  pupils  the  teacher  will  find  it  only  necessary  to  give 
a few  simple  directions,  and  provide  material  and  apparatus, 
the  pupils  will  do  the  rest. 


6 


EXPERIMENTAL  STUDIES  OF  PLANT  GROWTH. 


I.  General  Study  of  Germination. 

(a)  Under  favorable  conditions. 

Plant  some  radish  seeds  in  pot  of  sand  or  garden 
soil.  The  depth  of  planting  should  not  be  over  one- 
fourth  inch.  Keep  seeds  in  warm  place  and 
sprinkle  with  water  each  day. 

(b)  Lacking  water. 

Prepare  some  more  seeds  in  the  same  way  but  use 
dry  soil  and  do  not  add  water. 

(c)  Lacking  warmth. 

Prepare  and  care  for  seeds  as  in  (a)  but  keep  in  a 
cool  place.  If  weather  is  cool  the  seeds  may  be 
left  out  of  doors.  If  weather  is  warm  keep  in 
a refrigerator  or  in  ice-box  made  after  the  plan  il- 
lustrated in  Fig.  1. 

(d)  Lacking  air. 

Put  some  seeds  in  bottle  and  then  fill  with  water 
that  has  been  boiled  (to  drive  out  air)  and  cooled. 
Cork  tightly  and  seal  by  running  paraffine  around 
the  cork.  Keep  in  warm  place. 


1.  Arrangement  for  keeping  seeds  on  ice:  the  space  be- 
tween the  boxes  is  filled  with  sawdust,  which  also 
surrounds  the  ice. 


When  seeds  have  germinated  in  (a)  examine  seeds  in 
(b),  (c)  and  (d),  and  compare  with  growth  in  (a).  The 


7 


results  observed  will  indicate  conditions  necessary  for  germi- 
nation of  seeds  viz.,  water,  warmth  and  air. 

II.  Vitality  of  Seeds. 

Even  under  favorable  conditions  some  seeds  will  not 
germinate.  It  is  important  before  planting  a large  number 
of  seeds  to  test  them  to  see  what  per  cent  will  germinate. 
Test  the  seeds  of  the  ears  of  corn.  Make  a tester  out  of  small 
cigar  box.  For  details  of  making  the'test  see  5,  P.  59,  and 
4,  Fig  7. 

III.  Decay  of  Seeds. 

Seeds  that  germinate  slowly,  especially  if  they  are 
large,  often  decay  instead  of  germinating.  This  is  due  to 
the  action  of  bacteria  and  m.oulds.  The  value  of  formalde- 
hyde in  preventing  this  action  may  be  shown  as  follows : 

(a)  Cover  ten  beans  with  a one  per  cent  solution  of 
formaldehyde  for  one  hour.  After  rinsing  them  to  re- 
move the  formaldehyde  put  them  in  a tumbler  of  v/ater 
and  leave  in  a warm  place. 

(b)  Ten  other  beans  that  have  not  been  treated  with 
formaldehyde  should  be  left  in  a tumbler  of  water  as  in 
(a).  After  two  or  three  days  compare  (a)  and  (b).  The 
first  stages  of  decay  will  be  indicated  by  cloudiness 
of  the  water.  If  left  long  enough  the  seeds  in  (a) , pro- 
vided there  is  air  enough  in  the  water,  will  germinate. 
Those  in  (b)  will  decay. 

IV.  Structure  of  Typical  Seeds. 

To  facilitate  study  of  seeds,  they  should  be  left  in  water 
over  night  or  longer. 

(a)  Lima  bean. 

1.  Note  markings  on  surface : 

a.  Scar  or  hilum  where  seed  was  attached  to  pod. 

b.  Near  hilum  on  middle  line  of  bean  a small  opening, 
the  micropyle, 

2.  Remove  the  covering,  seed-coat  or  testa.  Near  the 
hilum  a small  pointed  body,  the  caidicle  will  be  seen. 
Note  its  position  with  reference  to  the  micropyle. 


8 


Separate  the  halves  or  cotyledons,  observe  that  the 
caulicle  bears  two  small  leaves,  the  plumule. 

The  cotyledons,  caulicle  and  plumule  constitute  the 
embryo, 

(b)  Castor-bean. 

1.  Remove  the  testa  and  note  the  inner  seed-coat,  the 
endopleura  which  encloses  the  kernel. 

2.  Expose  the  embryo  by  split- 
ting the  kernel  longitudinal- 
ly. Make  out  the  parts  as 
shown  in  Fig.  2:  (c)  cauli- 
cle; (si)  cotyledons;  (e)  en- 
dosperm; (ca)  caruncle,  a 
protuberance  on  testa. 

3.  The  material  of  the  kernel 
surrounding  the  embryo  is 
the  endosperm. 


2.  Castor-bean  open,  showing  en- 
dosperm (e),  caulicle  (c), 
seed-leaves  {si)  and  caruncle 

(ca). 


(c)  Corn.  (A  grain  of  corn  is  a fruit,  not  a true  seed.) 

1.  Note  general  shape.  The  groove  on  one  side  marks 
position  of  embryo. 

2.  Cut  grain  lengthwise  so  as  to  show  parts  as  indicated 
in  Fig.  3. 

Make  out  the  parts  by  comparing  cut  surface  with  Fig. 
3:  (c)  caulicle;  (pi)  plumule  (1) 
seed-leaf  or  cotyledon;  (e)  en- 
dosperm. 

All  seeds,  except  the  seeds  of  con- 
ifers, are  of  one  of  these  types.  In 

(a)  the  food  material  is  stored  in  the 
cotyledons  of  the  embryo  itself ; in  (b) 
and  (c)  the  food  material  is  stored  out- 
side of  the  embryo  and  is  called  en- 
dosperm. 

Drawings  should  be  made  of  (a), 

(b) ,  and  (c)  showing  and  naming 
parts. 


Corn  cut  lengthwise,  show- 
ing cavilicle  (c).  Plumule 
{pD,  seed-leaf  (/)  and 
Endosperm  (e). 


V.  Balance. 


In  order  to  perform  several  of  the  experiments  outlined 
a balance  will  be  necessary.  If  it  cannot  be  bought  one  may 


9 


be  easily  constructed  from  a rib  of  an  old  umbrella  as  shown 
in  Fig.  4.  The  rivet  which  unites  the  long  and  short  arms 
of  the  wire  should  be  taken  out,  and  a fine  needle  used  in  its 
place.  Tops  of  baking  powder  cans  will  make  good  pans. 
These  should  be  attached  as  shown  in  figure  by  means  of  silk 
thread  or  fine  wire.  The  two  arms  of  balance  should  be 
exactly  the  same  length,  and  points  of  attachment  for  the 


4.  A home-made  balance  constructed  of  umbrella  wire;  it  can  be  made  sensatve 
to  a tenth  of  a gram. 


pans  should  be  equi-distant  from  the  needle.  The  two  sides 
may  be  made  to  balance  by  trimming  edges  of  pans.  Metric 
weights  should  be  bought  if  possible.  Weights  may  be  made 
by  trimming  pieces  of  lead  to  correspond  to  the  weights  of  a 
druggist. 

Another  way  of  making  a balance  is  described  in  5,  Pp. 
28-30. 


VI.  Relation  of  the  Micropyle  to  Absorption 
of  Water. 

1.  Put  a dry  bean  in  a flask  or  test-tube  partly  filled 
with  water.  Heat  gently  over  a gas  or  alcohol  flame. 
Heat  expands  air  within  the  bean.  Note  where  the 
air  escapes  as  indicated  by  small  bubbles  leaving  the 
seed. 

2.  Gently  press  a seed  that  has  been  soaked  several  hours 


lO 


in  water,  and  note  if  water  is  forced  out  at  same 
point  as  the  air  in  1. 

3.  Select  thirty  grains  of  corn.  Fill  a cigar  box  two- 
thirds  full  of  sand,  and  keep  it  moist  during  the  pro- 
gress of  the  experiment. 

Place  seeds  in  rows  of  10  each  as  follows : 

Row  1,  with  points  of  seeds  inserted  in  sand. 

Row  2, "with  broad  end  of  seed  in  sand. 

Row  3,  with  five  seeds  lying  on  smooth  side  and  five 
lying  on  side  with  groove. 

Note  time  of  germination  of  seeds  in  each  row  and  ac- 
count for  the  difference  noted.  Remember  that  the 
opening  in  the  corn,  corresponding  to  the  micropyle 
in  function  , is  at  the  pointed  end. 

VII.  Water  and  Germination. 

In  the  preliminary  studies  of  germination  (I),  it  was 
found  that  seeds  would  not  germinate  without  water.  Our 
first  problem  is  to  determine  more  exactly  the  relation  of 
water  to  the  germinating  seed.  Does  water  enter  the  seed? 

Weigh  two  beans  of  nearly  the  same  size.  Put  one  (a) 
in  water,  and  leave  the  other  (b)  dry.  After  24  hours  com- 
pare (a)  with  (b):  (1)  as  to  weight;  (2)  as'tosize,  by  tracing 
outline  of  each  on  paper. 

VIII.  Changes  in  Appearance  of  Seed  During 
Absorption  of  Water. 

Place  lima  bean  in  water  and  observe  at  intervals  of 
one  hour  for  several  hours.  A drawing  should  be  made  at 
each  observation  showing  appearance  at  that  time.  Fig.  5. 


5.  A Bean  placed  in  water,  showing  successive  stages  in  the  process  of  wrinkling;  the 
wrinkling  indicates  where  the  water  enlers  and  how  it  spreads  inside  the  cover. 


IX.  Absorption  of  Water  by  the  Seed. 

Select  10  seeds  (beans)  of  nearly  the  same  size  and 
weight.  Divide  them  into  sets  of  five.  Designate  the  sets 
as  (a)  and  (b).  Weigh  each  set. 


II 


1.  Cover  seeds  of  (a)  entirely  with  water. 

2.  Arrange  seeds  of  (b)  in  water  so  that  the  hilum  of 
each  seed  will  be  exposed  and  free  from  contact  with 
water.  Seeds  may  be  held  in  position  with  hilum  up 
by  means  of  a strip  of  bent  lead  or  tin  (U  shape)  or  by 
means  of  a piece  of  coiled  wire  as  shown  in  Fig  6. 
Care  should  be  taken  in  the  selection  of  seeds,  avoid- 
ing seeds  that  have  injured  seed-coats. 


6.  An  arrangement  for  holding  seeds  while  under  water. 


After  from  four  to  six  hours  carefully  weigh  (a)  and  (b). 
Before  weighing  water  must  be  carefully  drained  off,  and 
seeds  dried  by  means  of  blotting  paper  or  cloth. 

A comparison  of  (1)  with  (2)  will  show  that  most  of  the 
water  enters  in  the  region  of  the  micropyle  and  that  part 
enters  through  the  seed-coat. 

X.  Absorption  of  Water  Through  the  Seed-Coat. 

Remove  the  seed-coats  of  several  pumpkin  seeds.  Each 
seed-coat  should  be  in  nearly  entire  halves  and  free  from 
openings  or  cracks. 

Into  each  half  of  seed-coat,  thus  prepared,  put  a few  crystals 
of  sugar.  (There  should  be  at  least  six  halves. ) Arrange 
part  of  them  on  water  so  as  to  float  like  boats;  put  the 
rest  on  a dry  surface  as  a control  experiment.  If^the  seed- 
coats  permit  water  to  pass  through  this  fact  will  be  indicat- 
ed by  the  sugar  dissolving. 

The  rate  that  the  sugar  crystals  pass  into  solution  is  a 
rough  measure  of  the  passage  of  water  through  the  seed- 
coat.  Compare  rate  in  seed-coats  of  several  kinds  of  seed : 
pumpkin,  caster  bean,  almond,  walnut  and  other  large  seeds. 
If  difference  of  rates  is  noticed,  tabulate  results. 

XL  Importance  of  Embryo  or  Endosperm  in  Absorption 
of  Water  Through  the  Seed-coat. 

Prepare  several  seed-coats  as'  in  X but  use  pieces  of 
embryo  (or  endosperm  in  such  seeds  as  castor  bean)instead  of 


12 


sugar  crystals.  Weigh  pieces  of  embryo  or  endosperm  at  be- 
ginning of  the  experiment,  and  at  one  hour  or  longer  inter- 
vals  to  determine  whether  or  not  water  is  absorbed. 

XIL  Course  of  Water  on  Entering  the  Seed. 

Put  seeds  in  some  red  ink  or  solution  of  eosin  (red  dia- 
mond dye  may  be  used. ) Several  seeds  should  be  used.  Re- 
move a seed  at  one-half  to  one  day  intervals.  Examine  by 
splitting  seed  and  noting  portions  colored.  Make  diagram. 
Observe  relation  the  path  of  water  seems  to  have  to  the 
embryo  plant.  (Caulicle  in  case  of  bean,  and  other  seeds 
having  fleshy  cotyledons.) 

XIII.  Amount  of  Water  Necessary  for  Seeds 
to  Germinate. 

In  each  of  several  pint  or  quart  mason  jars  put  ten  dry 
bean  seeds.  Cover  with  dry  sand  to  depth  of  one-half  inch. 
Number  (1),  (2),  (3),  (4),  etc.  Add  small  quantity  of  water 
(5  cubic  centimeters)  to  (1) ; twice  as  much  to  (2) ; three 
times  as  much  to  (3) ; etc. 

The  beginning  of  germination  will  be  noted  when  the 
caulicle  begins  to  make  its  appearance. 

The  amount  of  water  put  in  the  jar  where  seeds  first  as- 
sume above  appearance  (caulicle  protruding)  is  approximate- 
ly the  minimum  amount  of  water  needed  for  germination. 
Remove  one  of  the  seeds  that  is  just  germinating;  weigh; 
drive  off  moisture  by  means  of  heat;  weigh  until  weight  is 
constant.  From  these  weights  determine  the  amount  of 
water  in  the  seed  when  the  caulicle  appears.  Determine 
also  per  cent  of  water  in  seed  at  this  stage  of  germina- 
tion. 


XIV.  Effect  of  Moist  Air  on  Germination  of  Seed. 

Using  a mason  jar,  cover  the  bottom  with  water  and 
support  some  seeds  (radish  and  beans)  by  means  of  wire 
netting  as  shown  in  Fig.  7.  As  this  experiment  must  be 
under  observations  several  weeks,  it  will  be  necessary  to 
treat  the  seeds  with  formaldehyde  to  prevent  mould. 

It  is  desirable  also  to  weigh  the  seeds  before  putting 
them  in  the  jar.  At  conclusion  of  experiment  (i.  e.  after 


13 


4-6  weeks)  weigh  seeds,  and  compare  with  original  weight. 
Calculate  amount  of  water  absorbed.  Some  seed-coats,  e.  g. 
those  of  radish  seeds  absorb  water 
readily. 

If  seeds  germinate  in  moist  air, 
it  is  important  that  they  be  stored 
in  a dry  place. 

XV.  Amount  of  Air  Necessary 
for  Germination. 

We  have  already  seen  in  exer- 
cise I that  air  is  rkeeded  for  seeds 
to  germinate. 

Partly  fill  six  homo-vials  with 
sand,  at  different  depths  ranging 
from  one-half  inch  in  first  to 
within  less  than  one-fourth  inch  of 
top  in  last.  Do  not  leave  any  free 
water  above  the  sand.  When  seeds 
begin  to  germinate  in  any  of  the 
vials  examine  the  others. . 

XVI.  Test  for  Carbon  Dioxide. 

We  are  familar  with  the  fact  that  animals  need  air  (ox- 
ygen), and  that  in  breathing  (respiration)  they  give  off  car- 
bon dioxide. 

Prepare  limewater  as  follows : Pour  water  on  unslack- 
ed lime  and  allow  to  stand  several  hours.  Filter  the  liquid 
or  strain  through  cotton.  Keep  liquid  (limewater)  in  a 
well  stoppered  bottle.  When  carbon  dioxide  comes  in  con- 
tact with  lime  water,  the  solution  becomes  cloudy.  Carbon 
dioxide  unites  with  the  lime  making  insoluble  carbonate  of 
lime.  Test  air  from  lungs  for  carbon  dioxide  by  blowing 
breath  through  glass  tube  into  a bottle  of  limewater.  Note 
cloudy  or'milky  appearance  of  liquid.  This  is  a common  test 
for  carbon  dioxide. 


7 Seeds  placed  in  a saturated 
atmosphere. 


14 


XVII.  Carbon  Dioxide  Given  Off  by  Germinating  Seeds. 

Put  a quantity  of  soaked  peas  or  beans  in  a mason  jar 
with  a vial  of  lime  water  (leave  vial  open),  and  seal  jar 
tightly.  For  control  experiment,  ar- 
range another  jar  with  vial  of  lime 
water  surrounded  by  cotton  or  paper 
instead  of  seeds.  For  arrangement 
of  experiment  see  Fig.  8. 

After  24  hours  examine  the  lime- 
water  in  the  two  jars.  If  water  in 
the  control  experiment  is  clear  or 
nearly  so,  and  that  in  the  other  jar  is 
covered  with  a thin  white  crust  and 
the  water  itself  somewhat  milky  in 
appearance,  we  must  conclude  that 
carbon  dioxide  has  been  given  off  by 
the  germinating  seeds. 


. Apparatus  foi  determining 
whether  germinating  seeds 
produce  carbon  dioxide, 
the  vial  is  filled  with  lime- 
water.  (Seen  in  section.) 


XVIIL  Amount  of  Carbon  Dioxide  Given  off  During 
Germimation, 

The  amount  of  carbon  dioxide  given  off  by  a certain 
mass  of  seeds  in  a certain  time  (24  hours)  may  be  roughly 
shown  as  follows: 

1.  Carefully  fit  a glass  tube  into  each  stopper  of  two 
wide-mouthed,  6 ounce  bottles.  The  stoppers  must  fit 
closely  to  tubes  and  bottles  so  that  no  air  can  enter 
bottles  except  through  glass  tubes.  If  rubber  stoppers 
of  the  right  size  are  used  they  will  probably  fit  with- 
out any  extra  precaution.  If  cork  stoppers  are  used 
they  should  be  soaked  in  melted  paraffin,  and  after  the 
glass  tubes  are  inserted  melted  paraffin  should  be  ap- 
plied around  them.  In  each  bottle  the  glass  tube 
should  extend  from  about  two  inches  outside  nearly  to 
the  bottom  on  the  inside. 

2.  Fill  two  glass  tumblers  to  a depth  of  one  inch  with 
strong  solution  of  lye  (caustic  soda  or  caustic  potash.) 

3.  Fill  one  bottle  to  a depth  of  about  two  inches  with 


15 


germinating  seeds.  Seeds  that  have  been  soaking  over 
night  will  do. 

4.  Cork  both  bottles  tightly  with  stoppers  prepared  as  in 
(1).  Be  careful  that  no  air  may  enter  at  edge  of  stop- 
per or  around  the  glass  tube  of  either  bottle. 

5.  Invert  each  bottle  over  a glass  of  lye  (2)  so  that  the 
end  of  the  tube  beyond  the  outside  of  stopper  will  re- 
main below  surface  of  lye.  Secure  bottle  to  glasses 
by  means  of  clamps  and  of  pieces  of  string  or  rubber 
bands. 

The  arrangement  of  apparatus 
is  shown  in  Fig  9.  Lye  (caustic 
potash  or  caustic  soda)  absorbs  car- 
bon dioxide.  If  carbon  dioxide  is 
given  off  by  the  germinating  seeds, 
it  will  be  absorbed  by  the  lye-  The 
lye  will  therefore  rise  in  the  glass 
tube  in  proportion  to  the  amount  of 
carbon  dioxide  dissolved.  This 
amount  is  the  amount  given  off  by 
the  seeds.  The  empty  bottle  and 
solution  of  lye  is  a control  experi- 
ment. The  cubic  capacity  of  the 
glass  tube  above  the  level  of  the 
lye  to  the  point  where  the  lye  ascends  represents  approxi- 
mately the  volume  of  carbon  dioxide  given  off  during  the  op- 
eration of  the  experiment.  If  left  longer  than  24  hours  the 
lye  will  probably  be  drawn  into  the  bottle  with  the  seeds. 

Note— If  air  in  the  room  is  very  warm  when  the  control 
experiment  is  prepared,  and  afterwards  becomes  cool,  the 
air  in  the  bottle  will  contract.  Under  such  conditions  the 
lye  will  be  drawn  up  into  the  tube  and  possibly  over  flow 
into  the  bottle.  The  experiment,  therefore,  should  be  prepar- 
ed in  a cool  place. 

XIX.  Effect  of  Drying  on  Subsequent  Growth  of 
a Germinated  Seed* 

Allow  several  grains  of  corn  or  wheat  to  germinate  until 
caulicle  is  plainly  seen.  Separate  into  sets  of  5 grains  each. 
Allow  first  set  to  dry  24  hours;  the  second,  48;  the  third,  72; 

i6 


9,  Method  of  measuring  the  amount 
of  carbon  dioxide  produced  by 
germinating  seeds,  the  tumblers 
contain  lye  (control  at  the 
right). 


the  fourth,  96;  at  the  end  of  these  periods  restore  seeds  to 
favorable  conditions. 

Note  minimum  time  seed  may  be  exposed  to  dryness 
without  preventing  subsequent  growth. 

XX.  Influence  of  Depth  of  Planting  on  Germination. 

Fill  a quart  mason  jar  to  depth  of  one  inch  with  garden 
soil  and  place  seed  next  to  glass ; add  another  inch  of  soil  and 
plant  the  second  seed;  and  soon  until  the  topis  reached. 
The  soil  should  be  packed  tightly  around  the  seeds.  Keep  the 
soil  moist  and  the  jar  covered  so  as  to  exclude  the  light. 

At  end  of  one  week  or  ten  days  make  note  of  progress 
of  germination  and  growth.  (5,  P.  56.) 

XXL  Influence  of  Seed-coat  on  Germination. 

Select  twelve  seeds  of  each  of  several  kinds  (pumpkin, 
sweet-pea,  four  o’clock,  peach,  walnut,  etc.)  With  each 
kind  of  seed  proceed  as  follows:  Plant  6 seeds  in  moist  soil; 
6 seeds  in  moderately  dry  soil.  Do  the  same  with  the  other 
six  seeds  having  previously  removed  the  seed -coats. 

Note  effect  of  removal  of  seed-coats  on  time  of  germina- 
tion of  each  kind  of  seed. 

Note  also  any  other  effect  of  removal  of  seed-coats  as  in- 
dicated by  difference  in  results. 

XXII.  Work  Performed  by  Germinating  Seeds. 

Fill  bottle  with  dry  seeds  and  add  as  much  water  as  bot- 
tle will  hold.  Cork  tightly  and  secure  stopper  by  means  of  a 
wire.  Set  away  24  hours  and  note  result. 

The  force  exerted  by  germinating  seeds  in  first  stage  of 
germination  (period  of  water  absorption)  may  be  measured. 

Fill  fruit  press  half  full  of  dry  seeds.  Attach  spring 
balance  to  arms  of  press  so  that  any  movement  of  arms  will 
be  recorded  by  balance.  Method  of  setting  up  experiment 
will  be  readily  seen  by  consulting  Fig.  10.  Place  lower  parts 
of  press  in  water.  After  two  hours  read  pressure  as  indi- 
cated by  balance.  After  24  hours  take  another  reading. 

Calculate  area  of  piston  of  press,  and  from  the  arms  of 
press  as  levers  calculate  pressure  exerted  by  1 square  inch 
surface  of  the  mass  of  germinating  seeds.  The  pressure 


17 


exerted  at  (b)  which  is  the  amount  exerted  on  piston)  is  equal- 
to  distance  in  inches  from  (a)  to  (c)  times  weight  indicated 
by  balance,  divided  by  distance  in  inches  from  (a)  to  (b). 


10.  Appratus  for  demonstrating  that  swelling  seeds  exert  pressure  (a  portion 
of  the  wall  is  represented  as  cut  away  in  order  to  show  the  seeds) . 


In  levers  the  distance  of  the  power  from  fixed  point  times 
power  is  equal  to  distance  of  weight  from  fixed  point  times 
weight. 

XXIIL  Heat  Generated  by  Germinating  Seeds* 

Although  the  rise  in  temperature  in  germinating  seeds 
is  slight, it  may  be  measured— provided  conditions  are  favor- 
able and  great  care  is  taken. 

Test  two  thermometers  to  see  if  their  readings  are  the 
same  when  place  side  by  side  in  (a)  cool  water,  and  (b)  in 
warm  water.  If  they  do  not  register  the  same,  allowance 
must  be  made  for  this  difference  in  subsequent  readings. 

Fill  a tumbler  ( a)  with  seeds  that  have  been  soaking 
about  24  hours.  Fill  another  tumbler  (b)  with  damp  cotton. 

Fit  a thermometer  in  the  center  of  a cardboard  cover  for 
each  tumbler.  The  bulbs  of  the  thermometers  should  extend 

i8 


to  the  center  of  the  contents  of  the  tumblers.  The  apparatus 
with  thermometers  in  place  is  shown  in  F‘g.  11. 


11.  Method  of  measuring  the  temperature  of  germinating  geeds. 
(control  at  right). 


Take  reaciings  every  10-20  minutes.  If  there  is  a slight 
rise  of  temperature  in  (a)  and  no  rise  in  (b)  the  difference 
must  be  due  to  heat  of  germinating  seeds.  The  amount  is  not 
likely  to  be  over  one  degree. 

XXIV.  Importance  of  Cotyledon  or  Endosperm. 

1.  Germinate  several  grains  of  com  and  beans  until 
caulicles  appear. 

2.  Fill  two  boxes  with  garden  soil.  Plant  in  one  (a)  two 
grains  of  corn,  and  two  beans. 

Cut  off  part  of  the  endosperm  of  two  grains  of  corn 
and  part  of  the  cotyledons  of  two  of  the  beans.  Plant 
these  in  pot  (b). 

Give  each  pot  the  same  care  as  to  water  and  warmth. 
Keep  theTplants  as  they  appear  under  observation  for 
at  least  two  weeks,  taking  notes  of  appearance  and 
making  measurements  from  time  to  time.  The  results 


19 


of  this  exercise  should  show  the  importance  of  the 
stored  up  food  supply  in  the  seed. 

The  importance  of  this  may  be  further  shown  by 
selecting  seeds  of  different  sizes.  Plant  them  and 
keep  growing  under  favorable  conditions.  Observe 
differences  in  growth.  These  differences,  in  the  ear- 
ly stages,  will  be  due  chiefly  to  difference  in  the 
amount  of  food  stored  up  in  the  seeds.  Consult  Fig- 
ure on  page  10  of  3. 

XXV.  Test  for  Starch. 

Starch  is  one  of  the  most  important  forms  of  food  stored 
up  seeds.  Its  presence  may  be  easily  detected  by  means  of 
a solution  of  iodine. 

Make  a little  starch  paste  by  rubbing  up  a small  quan- 
tity of  starch  in  cold  water  and  then  adding  hot  water.  Di- 
lute and  add  a few  drops  of  solution  of  iodine.  The  blue 
color  that  appears  indicates  the  presence  of  starch. 

Test  several  kinds  of  seeds  for  starch.  The  best  results 
will  be  obtained  by  first  grinding  seeds  into  a powder  (by 
means  of  a mortar)  and  then  preceding  as  in  making  starch 
paste. 

XXVI.  Test  for  Grape  Sugar. 

The  presence  of  grape-sugar  may  be  detected  as  follows : 
Dissolve  a small  amount  of  grape-sugar  in  a test-tube.  Add 
a few  centimeters  of  Fehling^s  solution  and  boil  over  gas  or 
alcohol  flame.  A reddish  precipitate  will  be  formed.  The 
formation  of  this  precipitate  after  the  above  procedure  in- 
dicates the  presence  of  grape-sugar  in' the  substance  tested. 

XXVIl.  Digestion  of  Starch. 

Starch  is  a solid.  It  must,  therefore,  be  changed  into  a 
soluble  form  before  the  developing  plant  can  use  it,  or  before 
it  can  be  transferred  from  one  place  to  another.  In  other 
words,  it  must  be  digested.  When  starch  is  digested  it  is 
changed  to  grape-sugar.  The  digestion  of  starch  in  germi- 
nating seeds  may  be  demonstrated  as  follows: 

(a)  Grind  up  in  mortar  with  water  several  wheat  or  barley 
seeds.  Pour  off  milky  liquid  and  test  for  grape  sugar 
as  in  XXVI. 


20 


(b)  Grind  up  several  of  the  same  kind  of  seeds  as  in  (a) 
that  have  germinated  far  enough  for  caulicle  to  be 
easily  seen.  Pour  off  liquid  and  test  for  grape  sugar. 

XXVIIL  Endosperm  and  Cotyledons  After  Seedlings 
Have  Become  Established. 

In  preparation  for  this  study  a number  of  grains  of  corn 
and  beans  should  be  planted  in  a box  (cigar  box)  containing, 
good  garden  soil.  Keep  under  favorable  conditions  for  ger- 
mination and  growth. 

At  intervals  of  one  week  after  the  seedlings  have  ap- 
peared pull  up  one  of  each  kind.  Note  appearance  with  re- 
ference [to  amount  of  endopserm  in  the  corn,  and  size  of 
cotyledons!  in  beans.  Note  also  condition  of  plant  as  to  ex- 
tent of  roots  and  leaves  at  time  when  food  supply  appears 
exhausted. 


XXIX.  Lifting  Power  of  a Growing  Seedling. 

It  is  important  for  the  seedling  in  becoming  established 
to  push  its  leaves  above  the  ground.  It  must  do  this  in  order 
to  be  ready  to  make  its  own  food  before  the  food  supply 
stored  up  in  the  seed  is  exhaust- 
ed. This  process  often  requires 
considerable  force,  especially 
when  the  surface  of  the  ground 
is  hard.  The  lifting  power  of 
the  growing  stem  may  be  meas- 
ured by  having  it  lift  a weight. 

One  of  the  plants  grov/ing  in 
box  prepared  in  XXVIII  may  be 
used. 

As  soon  as  it  appears  about 
one  inch  above  the  ground  ar- 
range apparatus  as  shown  in  Fig. 

12.  The  larger  bottle  (a)  (about 
one  inch  in  diameter)  should  be 
cut  off  at  bottom  and  top  so  as  to 
make  a tube  of  uniform  diam- 
eter. (Make  a scratch  around 

glass  bottle  with  a file-  A quick  ^ , 

- , Ml  ji  11  1 11  Apparatus  for  measuring  the  force 

blow  Will  then  usually  break  the  of  the  upward  growth  of  the  plant. 


21 


bottle  at  the  desired  place.)  A tube  made  from  a large 
test-tube  is  easier  to  prepare.  The  smaller  bottle  (b)  should 
fit  easily  into  the  tube  made  from  the  larger  one. 

Put  (a)  over  plant,  protecting  the  plant  with  small  wad 
of  cotton,  and  insert  (b)  in  (a)  as  shown  in  figure*  Partly 
fill  (b)  with  shot.  A narrow  slip  of  paper  should  be  pasted 
vertically  on  side  of  (a)  and  a mark  made  at  the  level  of  the 
bottom  'of  the  inner  bottle.  As  the  plants  grow  upward  it 
must  lift  the  weight.  A daily  record  of  the  height  should  be 
indicated  by  mark  on  strip  of  paper.  The  work  done  may 
be  estimated  in  terms  of  gram-centimeters.  (Vertical  dis- 
tance in  centimeters  times  weight  of  bottle  plus  shot  and  cot- 
ton) , or  in  terms  of  pressure  reduced  to  grams  per  sq.  cm. 
or  pounds  per  square  inch  i.  e.  pressure  that  would  be  exert- 
ed if  the  stem  had  1 sq.  cm.  or  one  sq.  in.  cross  section. 
This  may  be  found  by  the  formula: 

Weight 


3.1416  X R2  of  stem 

Osterhout  found  that  a plant  one-eighth  inch  in  diame- 
ter exerted  a pressure  (lifted  a weight)  of  one  pound.  This 
is  at  the  rate  of  81.5  pounds  per  square  inch,  a little  greater 
than  the  usual  pressure  in  boilers  of  ordinary  stationary  en- 
gines.   


.11 

13.  Bean  with  the 
stem  marked,  in 
order  to  deter- 
mine the  region  of 
greatest  growth. 


After  trying  this  experiment  with  one 
plant  it  should  be  repeated  with  others,  in- 
creasing weights  each  time  so  as  to  find  the 
maximum  weight  that  may  be  lifted. 

XXX.  Region  of  Growth  of  Stem  and  Root. 

The  pressure  exerted  by  the  plant  in  the 
previous  experiment  was  a growth-pressure. 
Where  this  growth  takes  place  may  be 
shown  as  follows : 

Carefully  remove  one  of  the  plants  grow- 
ing in  box  prepared  in  XXVIII  and  by  means 
of  a fine  thread  (a  strand  of  silk  is  best) 
which  has  been  dipped  in  India  ink  mark 
stem  of  plant  at  regular  intervals  (2  mm.  or 
1-8  in. ) See  Fig.  13.  The  roots  may  also  be 
marked  in  same  way.  Place  roots  of  plant 


22 


between  folds  of  moist  cloth  or  blotting  paper.  Make  daily 
examinations  of  plant.  Note  where  growth  takes  place  in 
stem  and  roots  as  indicated  by  distance  between  marks,  at 
time  of  observation,  as  compared  with  orignal  distance.  An 
illustrated  account  of  this  experiment  is  given  in  5, 
Pp.  25-26. 

XXXL  Other  Means  of  Plant  Propagation* 

Thus  far  growth  has  been  considered  only  with  refer- 
ence to  development  of  the  plant  from  seed.  Plants  are  also 
propagated  in  other  ways.  Whatever  the  method  of  pro- 
pagation (by  seed  or  other  means) , one  thingjis  essential,  viz. , 
a food  supply  to  draw  upon  while  the  new  plant  is  developing 
means  (roots  and  leaves)  to  shift  for  itself. 

The  following  forms  of  propagation  should  be  studied: 

1.  Stem  tubers,  e.  g.  potato. 

2.  Root  tubers,  e g.  sweet  potato. 

3.  Crown  tubers,  e.  g.  radish. 

4.  Bulbs,  e.  g.  onion 

5.  Corms,  e.  g.  gladiolus. 

6.  Layering,  e.  g.  raspberry. 

7.  Leaf  cuttings,  e.  g.  begonias. 

8.  Stem  cuttings,  e.  g.  geraniums. 

9.  Hard  cuttings  e.  g.  grape. 

10.  Grafting. 

11.  Budding. 

Suggestions  for  detailed  study  for  1,  2,  3,  4,  5,  will  be 
found  in  2 Pp.  31-35;  6,  7,  8,  9,  10,  11  in  5,  Pp.  34-42,  exer- 
cises 17-23;  6 should  also  be  consulted. 

XXXll.  Starch  and  the  Green  Leaf* 

We  have  found  that  the  growing  plant  uses  food  stored 
up  in  the  seed,  or  in  leaves,  stems,  bulbs  or  corms.  After 
the  plant  is  established,  and  its  food  supply  exhausted  it 
must  make  its  own  food. 

The  chief  food  making  organ  of  the  growing  plant  is  the 
green  leaf.  The  food  that  it  makes  is  starch. 

The  presence  of  starch  in  a leaf  may  be  detected  as  fol- 
lows : Remove  a leaf  that  has  been  in  sunlight  for  half  a 
day.  Put  leaf  in  boiling  water  for  a few  minutes,  and  then 


23 


in  alcohol  until  green  coloring  matter  (chlorophyll)  is  remov- 
ed. Test  for  starch  by  applying  iodine. 

XXXllL  Relation  of  Starch  Making  to  Sunlight. 

We  notice  that  leaves  are  always  held  toward  the  light; 
generally  so  that  direct  sunlight  may  reach  them  at  some- 
time during  the  day.  The  importance  of  sunlight  may  be 
shown  by  a simple  experiment:  Select  a leaf  that  is  well  ex- 
posed to  sunlight.  Shade  it  by  means  of  black  paper  for  a 
few  days.  Remove  the  shade,  and  cover  portion  of  the  leaf 
by  pinning  it  between  the  upper  and  lower  parts  of  a small 
paper  box  (a  round  pill  box  will  do).  The  method  of  fasten- 
ing illustrated  by  Fig.  16  is  convenient.  After  two  days  ex- 
posure to  sunlight  remove  the  leaf  and  test  for  starch  as  in 
XXV. 

The  relation  of  sunlight  to  starch  making  is  shown  by 
this  experiment  to  be  an  important  one.  Sunlight  is  neces- 
sary because  it  furnished  energy  to  the  leaf  for  this  work. 

XXXIV.  Composition  of  Starch. 

In  order  to  investigate  further  the  starch-making  pro- 
cess of  the  leaf  we  must  get  some  idea  of  what  starch  is 
composed. 

(a)  After  drying  starch  thoroughly,  to  drive  off  all  the 
free  water,  place  some  in  a dry  test-tube,  and  heat 
over  a gas  or  alcohol  flame.  In  a few  moments  mois- 
ture will  collect  on  sides  of  tube. 

(b)  Place  some  more  starch  in  a test-tube.  Insert  one 
end  of  a short  piece  of  glass  tubing,  bent  at  right 
angles,  into  a cork.  Fit  the  cork  into  the  test-tube 
containing  starch,  making  connections  air-tight. 
Heat  the  starch  as  in  (a)  but  while  heating  place  free 
end  of  glass  tube  in  glass  of  lime  water.  The  gases 
that  are  evolved  from  the  heat  will  pass  into  the  lime- 
water.  The  limewater  will  become  milky,  indicat- 
ing that  carbon  dioxide  has  been  driven  off  from  the 
starch. 

These  experiments  indicate  that  starch  contains,  at 
least,  elements  found  in  water  and  carbon  dioxide  viz.,  car- 
bon, hydrogen  and  oxygen.  More  exact  analysis  would  show 


24 


that  starch  is  a combination  of  these  elements  in  the  propor- 
tion of  C 6 H 10  0 s. 

XXXV.  Absorption  of  Carbon  Dioxide  by  the  Leaf. 

While  it  does  not  necessarily  follov/  from  the  experi- 
ments in  XXXV  that  starch  is  made  from  water  and  carbon 
dioxide,  we  are  justified 
in  trying  to  determine 
whether  they  are  used  by 
the  leaf  while  the  starch- 
making progress  is  goingon. 

The  fact  that  the  leaf  uses 
carbon  dioxide  may  be 
shown  by  means  of  an  ex- 
periment arranged  as  shown 
in  Fig.  14. 

An  empty  mason  jar  is  inverted  over  a lighted  candle 
floating  on  a cork  in  a basin  of  water.  When  the  candle 
goes  out  (due  to  exhaustion  of  oxygen)  it  should  be  with- 
drawn by  means  of  string  (previously  attached  to  it),  and  a 
leaf  substituted.  The  jar  should  not  be  lifted  at  any  tirn^ 
above  the  surface  of  the  water.  Another  jar  for  control,  but 
without  leaf,  should  be  used  in  same  way  as  the  jar  with 
leaf.  The  experiment  should  be  set  up  in  the  morning  on  a 
clear  day,  and  the  leaf  exposed  to  sunlight  for  several  ( six) 
hours.  Finally,  place  a piece  of  glass  over  the  mouth  of  the 
jar  containing  the  leaf.  Without  admitting  any  air  restore 
jar  to  upright  position.  Introduce  a lighted  candle.  If  it 
does  not  go  out  immediately,  and  no  air  has  been  admitted 
some  oxygen  must  have  been  set  free  in  the  jar  during  the 
exposure  of  the  leaf  to  sunlight.  The  most  probable  source 
of  this  oxygen  is  through  the  decomposition  of  carbon  dioxide 
(the  product  of  combustion  of  the  candle  in  the  first  part  of 
the  experiment)  by  the  leaf  while  in  sunlight. 


14.  Arrangement  for  investigating  the  power 
of  a leaf  to  “restore”  air  which  has  been 
“vitiated”  by  a burning  candle,  (Sec- 
tional view) , 


25 


15.  Arrangement  for  collecting  the  gas 
given  off  by  a water-plant  in  sun- 
light, 


XXXVL  Oxygfcn  Given  Off  by 

Green  Plant  in  Sunlight. 

Thislmay  be  shown  by  us- 
ing some  plant  that  grows  sub- 
merged in  water  (e.  g.  horn- 
wort)  and  arranging  it  be- 
neath a funnel  as  shown  in 
Fig  15.  The  funnel  is  filled  by 
placing  it  entirely  under  water 
and  stopping  narrow  end  tight- 
ly with  small  cork.  If  a plate 
of  glass  is  held  closely  over 
the  broad  end,  the  funnel  filled 
with  water  may  then  be  re- 
moved to  battery  jar,  and  set 
up  as  indicated  in  the  figure. 
Place  in  sunlight. 

When  the  neck  of  the  fun- 
nel is  filled  with  gas  remove 
cork  and  insert  glowing 
splinter.  If  the  glow  be- 
comes brighter  or  bursts  into 
flame,  it  indicates  that  the  gas 
is  rich  in  oxgyen.  If  the  ap- 
paratus is  kept  in  the  shade  no 
oxygen  will  be  evolved. 


XXX YII.  The  Amount  of  Oxygen  Given  Off  by  the  Plant 
Depends  Upon  Amount  of  Carbon  Dioxide  Absorbed. 


We  infer  from  XXXV  that  carbon  dioixde  is  used  by  the 
green  leaf.  We  make  this  inference  because  the  only  appar- 
ent source  of  the  oxygen  in  the  jar  is  from  decomposition  of 
the  carbon  dioxide.  Since  there  is  no  oxygen  in  the  control 
jar,  this  decomposition  must  be  through  action"of  the  leaf. 

In  order  to  be  sure  that  the  oxygen  given  off  by  the 
plant  depends  upon  the  carbon  dioxide  we  may  make  a 
further  test : 

This  test  depends  upon  the  fact  that  fresh  spring  or 


26 


well  water  usually  contains  an  abundance  of  carbon  dioxide 
and  also  that  the  presence  of  carbon  dioxide  may  be  detected 
by  use  of  limewater. 

Put  some  aquatic  plants  (hornwort  or  algae)  into  three 
glasses  or  jars:  (a)  filled  wityspring  or  well  water  that  has 
been  standing  overnight;  (b)  filled  with  fresh  spring  or  well 
water.  (To  make  the  results  more  certain  carbon  dioxide 
may  be  introduced  by  blowing  the  breath  into  the  water  by 
means  of  a glass  tube);  (c)  filled  with  distilled  water  (water 
boiled  and  cooled  will  do).  Set  glasses  in  sunlight.  Within 
an  hour  a few  gas  bubbles  will  be  seen  coming  from  the 
plant  in  (a);  many  gas  bubbles  in  (b);  no  gas  bubbles  in  (c). 
Test  the  water  in  the  three  glasses  for  carbon  dioxide  by 
means  of  a few  drops  of  lime  water;  (a)  will  show  a trace  of 
carbon  dioxide;  (b)  will  give  a decided  test;  (c)  will  show 
none. 

By  means  of  glass  tube  blow  the  breath  into  the  water 
of  (a)  and(  (c.  Set  glasses  in  sunlight  and  note  increase  of 
gas  bubbles  given  off  by  the  plants.  Here  w’e  see  a close 
relation  between  the  amount  of  carbon  dioxide  and  the  evo- 
lution of  oxygen  by  the  plant.  More  elaborate  experiments 
than  can  be  described  here  have  shown  that  carbon  dioxide 
is  broken  up,  that  carbon  is  retained  in  the  plant,  and  that 
oxygen  is  given  off.  The  source  of  carbon  in  the  starch  made 
by  the  plant  is  carbon  dioxide. 

XXXVIIL  Transphation. 


Starch  also  contains  hydrogen  and  oxygen.  We  know 
that  water  is  composed  of  these  elements,  and  also  that 
water  is  necessary  for  the  plant  to  grow. 

We  cannot  prove  by  a simple  experiment 
that  water  is  actually  used  by  the  green  leaf 
in  starch-making  but  we  can  show  that  water 
passes  through  the  leaf,  and  is  thus  available 
for  such  use.  The  passage  of  water  through 
the  leaf  into  the  air  is  called  transpiration. 

Without  removing  leaf  from  the  plant 
arrange  on  opposite  sides  of  leaf,  by  means 

of  bent  wire,  two  watch  crystals  (two  pieces  Arrangement  for 

of  glass  will  do)  as  indicated  in  Fig  16.  Seal  determining  wheth- 
the  edges  of  the  crystals  with  vaseline.  In  a vaporf""^*  offwater 


27 


short  time,  especially  if  the  glasses  are  cool,  vapor  of  water 
will  be  condensed  on  the  sides  of  the  glasses  next  to  the  leaf. 
Observe  the  side  of  the  leaf  giving  off  the  more  moisture. 

Another  method  for  showing  that  the  leaves  give  off 
moisture  is  given  in  5,  P.  23. 

XXXIX.  Determination  of  Amount  of  Transpiration. 

The  amount  of  water  given  off  by  a leaf  may  be  meas- 
ured as  follows:  Arrange  apparatus  as  illustrated  in  Fig. 
17.  The  bottle  should  be  filled  v/ith  water,  and  the  cork 
containing  leaf  and  bent  tube  forced  down  until  the  water 


17.  Apparatus  for  measuring  the  transpiration  of  a leaf  and 
the  degree  in  which  it  is  affected  by  sunlight,  wind, 
rolling  the  leaf.  etc. 


passes  into  the  horizontal  tube  nearly  to  the  second  bottle. 
As  soon  as  apparatus  is  set  up,  mark  the  end  of  the  hori- 
zontal column  of  water.  As  transpriation  goes  on  water  in 
he  tube  will  move  toward  the  bottle  holding  the  leaf.  After 
one-half  hour  measure  the  distance  through  which  column 
of  water  has  traveled. 

If  diameter  of  tube  is  known,  the  amount  of  transpiration 
of  a leaf  in  a given  time  may  be  calculated  (area  of  cross 
section  of  tube  times  length  of  water  column).  Dividing  the 
amount  thus  obtained  by  square  inches  of  surface  of  leaf 
will  give  the  amount  of  transpiration  per  square  inch. 

There  are  many  problems  that  may  be  solved  by  means 
of  this  simple  apparatus,  e.  g.  rates  of  transpiration  of 


28 


leaves  of  different  kinds  of  plants;  difference  in  transpira- 
tion between  old  and  young  leaves;  estimation  of  total 
amount  of  transpiration  of  an  entire  plant;  effect  of  sunlight 
on  rate  of  transpiration;  devices  in  transpiration,  such  as 
hairy  covering  of  leaf,  etc. 

XL*  Path  of  Water  in  the  Stem  of  a Plant. 

Water  must  reach  the  leaf  by  way  of  stem.  What  path 
does  it  take? 

Cut  off  a leafy  branch  of  a plant  (geranium),  and  place 
cut  end  in  solution  of  eosin  (5  Pp.  23  24).  After  an  hour  or 
more  cut  the  stem  a short  distance  above  the  lower  end. 

The  path  of  water  as  indicated  by  red  stain  will  be  seen 
in  Ithe  fibrous  portion  of  the  stem  (fibro-vascular  bundles). 
A closer  examination  will  show  that  the  central  portion  of 
each  bundle  is  stained  more  deeply  than  the  rest. 

Let  the  branch  stand  in  the  fluid  until  the  leaves  begin 
to  be  colored.  By  making  successive  cuts  in  stem  toward 
the  leaves,  the  path  of  water  will  be  found  to  extend  from 
the  fibrous  bundlesnnto  the^veins  of  the  leaf.  The  veins  are 
smaller  extensions  of  the  bundles  of  the  stem. 

XLl.  Path  of  Starch. 

Since  the  leaves  make  starch  v/hich  must  be  digested 
and  carried  to  the  lower  parts  of  the  plant  we  would  expect 
to  find  provision  Jnade  for  its  transference.  What  then  is 
the  path  of  the  starch? 

We  found  in  XXXI  that  some  plants  could  be  propa- 
gated by  means  of  hard  cuttings.  Such  plants  have  sufficient 
food  supply  stored  up  in  the  stem  to  supply  the  plant  while 
it  is  getting  a start. 

In  some  plants  like  the  willow  this  food  supply  is  largely 
starch.  If  v/e  make  a short  willow  cutting  about  six  inches 
long  and  girdle  it  just  above  the  lowest  bud  we  will  divide 
the  food  supply  into  unequal  parts,  thus  limiting  the  avail- 
able means  for  passage  ofjfood  to  the  central  or  woody  part. 
(The  cutting  is  girdled  by  removing  a ring  of  bark  about 
one-half  inch  wide,  laying  bare  the  wood).  Place  the  girdled 
cutting  in  a mason  jar  filled  v/ith  water.  In  a short  time  it 
will  start  to  grow.  If  the  food  supply  including  starch  is 


29 


carried  through  the  layer  of  bark  the  growth  will  be  unequal 
because  '"the  food  supply  in  the  parts  above  and  below  the 
girdle  are  funequal.  If  there  is  an  equal  growth  above  and 
below  the  girdle  the  food  must  And  a passage  in  the  w^oody 
portion  of  the  stem.  A similar  cutting  which  has  not  been 
girdled  should  be  placed  in  another  jar  as  a control  experi- 
ment. 

‘‘Ringing grape  vines  is  practiced  by  many  growers  to 
secure  earlier  maturity  and  larger  bunches  of  grapes.  A 
ring  of  bark  is  removed  from  the  bearing  arm  between  the 
main  vine  and  the  buds  which  are  to  produce  the  fruit  of 
the  season.  This  does  not  interfere  with  the  ascent  of  the 
sap,  which  passes  through  the  outer  ring  of  undisturbed 
wood;  but  it  does  prevent  the  return  of  the  food  which  has 
been  formed  from  the  sap  in  the  leaves.  Thus  parts  of  the 
branch  above  the  ring  can  draw  upon  all  the  food  formed  in 
the  leaves  of  that  branch,  none  of  it  passing  on  to  build  up 
the  parent  vine.  Consequently  the  over  fed  bunches  grow 
faster  and  become  larger  than  their  less  favored  mates;  but 
the  vine  itself  may  suffer,  and  size  may  be  added  and  early 
maturity  produced  at  the  expense  of  quality.”  * 

XLIL  Region  of  Growth  in  Woody  Stems, 

By  slipping  the  bark  from  a woody  stem  (especially  in 
spring  time)  a thin  layer  of  juicy,  mucilaginous  substance 
wil  be  seen.  This  is  the  cambium  or  growing  region  of 
the  stem. 

For  further  explanation  of  the  cambium  see  2,  P.  257. 


In  the  foregoing  exercises  very  little  attention  is  given 
to  the  root.  For  experimental  studies  of  plant  growth  in 
which  the  root  is  concerned,  consult  7. 


* Bui.  151,  New  York  Agricultural  Experiment  Station,  Geneva,  New 
York. 


30 


References. 

1.  Experiments  with  Plants.  By  W.  J.  V.  Osterhout,  pp  51 1.  New 

York:  Macmillan  Co. |i«25 

2.  Botany,  an  Elementary  Text-book.  By  E.  H.  Bailey,  pp  377. 

New  York:  Macmillan  Co. __J5i.io 

3.  Conditions  Necessary  for  Plants  to  Grow  Well.  Columbus,  Ohio, 

Agricultural  College,  Extension  Bui.  Vol.  I,  No.  8 Free. 

4.  Improvement  of  the  Corn  Crop.  Columbus,  Ohio,  Agricultural 

College,  Extension  Bui.  Vol.  II,  No.  7 Free. 

5.  Plant  Production,  Exercises  in  Elementary  Agriculture.  By  D. 

J.  Crosby,  Washington,  D.  C.,  U.  S.  Department  of  Agri- 
culture, Office  of  Experiment  Stations,  Bui.  No.  186. Free. 

6.  The  Propagation  of  Plants.  By  E.  C.  Corbett,  Washington,  D. 

C.,  U.  S.  Department  of  Agriculture.  Farmers’  Bulletin 
No.  157. 

7.  The  Soil  and  its  Relation  to  Plants.  By  B.  M.  Davis,  Oxford,  O., 

Miami  University,  Bui.  No.  3,  Ser.  VI. Free. 


31 


Material  and  Apparatus  With  Estimated  Cost. 


1.  Alcohol,  I pt. $ .50 

2.  Alcohol  lamp,  4 oz .20 

3.  Balance,  Chaslyn  (1906)  model 15.C0 

4.  Balance,  spring .15 

5.  Bottles,  4 or  6 oz,,  wide  month,  with  corks,  i doz .50 

6.  Bottles,  3 dr.  homo-vials,  with  corks,  3 doz,. .30 

7.  Boxes,  empty  cigar  and  chalk  boxes 

8.  Candles,  Paraffine,  2 .05 

9=  Clamps,  wooden  clothes  pins  with  spring,  i doz .10 

10.  Cotton,  I roll .10 

11.  Fehling’s  solution,  4 oz .25 

12.  Filter  paper,  in  sheets,  i quire .35 

13.  Funnel,  glass,  5 in .20 

14.  Fruit  press,  (fig.  ii) .25 

15.  Glass  tubing,  assorted  sizes,  yi  lb .20 

16.  Grape  sugar  (glucose)  X lb .05 

17.  Graduate,  cylinder,  50  ccm,  capacity .35 

18.  Iodine,  tincture,  i oz .15 

19.  Jars,  Mason,  i doz.  each  of  pts.  and  qts i.oo 

20.  Jars,  battery,  i gal.,  2 .70 

21.  Lime,  small  quantity 

22.  Lye,  concentrated,  i can .10 

23.  Mortar  and  pestle,  4 in.,  glass .25 

24.  Seeds,  a good  supply,  including  corn,  beans,  peas,  pumpkin, 

radish,  castor-bean,  sweet-pea,  walnut,  peach,  etc .50 

25.  Stoppers,  rubber.  No.  7,  4 with  i hole  and  4 with  2 holes i.oo 

26.  Test-tubes,  5 in.,  i doz. .20 

27.  Thermometers,  chemical,  2 i.oo 

28.  Tumblers,  common  glass,  i doz. .30 

29.  Vaseline,  small  bottle .05 

30.  Watch  glasses,  small,  X .10 

31.  Weights,  metric,  i set  (i  centigr.  to  20  gr.) .55 


Notk — Nos.  2,  12,  13,  15,  17,  20,  23,  25,  26,  27,  30,  31  may  be  obtained 
from  the  Columbia  School  Supply  Co.,  Indianapolis,  Ind.;  3 from  C.  H. 
Stoelting  Co.,  31-45  W.  Randolph  St.,  Chicago,  111.;  i,  5,  6,  ii,  16,  18,  28  at 
any  drug  store;  the  rest  at  a general  merchandise  store.  If  the  Chaslyn 
balance  (3)  is  bought  it  will  not  be  necessary  to  buy  a set  of  metric 
weights  (31). 


32 


